How to check the amount of effective bentonite in the sand molding machine
The wet casting of sand molding machine are usually supplements bentonite according to the wet compressive strength of the sand molding machine when it is working. If the amount of ash in the molding sand is too large and the amount of effective bentonite is insufficient, the wet compressive strength will still appear to be high. The performance of the molding sand becomes brittle, the mold release property is deteriorated, the gas permeability is lowered, and the water content at the same compacting rate is increased. Castings are prone to defects such as sand, sand, sand holes, and pores. Since the late 1950s, some people in the United States have drawn a grid pattern of straight lines and broken lines through a large number of wet compressive strength, water content, solidity rate and bentonite addition amount of sand. Later, the "bentonite" was renamed the more general "binder". From the grid diagram, the total binder content is called the available binder content (AB); it is also said that the amount of binder that actually acts as a bonding grit in the molding sand is called the working binder amount (WB). . The two calculations of AB and WB are derived from the grid diagram. Some foreign capital foundry factories in China also quote these calculation formulas, for example, the A-2 high-pressure modeling sand is calculated: AB=8.1~8.3%, WB=4.3～4.7%. Since the end of the 1980s, some people in the United States have considered that most of the wet sand contains pulverized coal. The bentonite content has exceeded 5 to 7% of the drawing, and the sodium bentonite and calcium bentonite are blended in different proportions. It is also dispersed to 4 to 5 sieves, and the mixing efficiency is improved. The grid map drawn is formed by extremely complicated curves, and AB and WB cannot be calculated by simple mathematical formulas. In addition, the bentonite and raw sand resources vary from country to country, making it more difficult to simply use the aforementioned grid maps and calculation formulas. Therefore, most factories at home and abroad have changed the effective bentonite content of sand by using methylene blue adsorption.
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